MELBOURNE, Australia — A conservation group that has vowed to disrupt Japan's annual whale hunt launched its Antarctic campaign Wednesday by renaming one of its ships after "Crocodile Hunter" Steve Irwin, the late environmental campaigner.

The U.S.-based Sea Shepherd Conservation Society says it will use whatever means necessary to block Japan from harvesting up to 50 humpbacks, 935 minkes and 50 fin whales in Antarctic waters as part of an oceanic research program that critics decry as commercial whaling in disguise.

Japan's fleet is en route to the Southern Ocean waters, while the Steve Irwin and crew left Melbourne on Wednesday.

Irwin's widow, Terri, threw her support behind the mission by giving Sea Shepherd permission to rename one of its two flagship vessels after her husband, the TV wildlife program host who died from a stingray attack off Australia's Great Barrier Reef in September 2006.

"Whales have always been in Steve's heart, and in 2006 he was investigating the possibility of joining the Sea Shepherd on part of its journey to defend these beautiful animals," Terri Irwin said in a statement.

The hulking black-and-red vessel, which flies a pirate flag featuring a skull over a trident and a shepherd's hook, had previously been named for the Canadian anti-whaling campaigner Robert Hunter.

Sea Shepherd has come under heavy criticism in recent years for engaging in violent tussles with the Japanese whaling fleet.

In February, Sea Shepherd clashed with a Japanese vessel, leaving the Robert Hunter with a 3-foot gash in its stern, during a violent confrontation that both sides blamed on the other party.

Japanese officials said the activists threw ropes and nets into the water to entangle the Japanese ship's propeller and prevent it from maneuvering, and threw smoke canisters and garbage onto the deck.

Sea Shepherd has not disputed this version of the events, but says it does not discuss the specifics of its activities at sea.

During the clash, two Sea Shepherd crew members went missing for several hours in a small inflatable boat but were later found safe.

The confrontation drew protests from Japan, and even sparked strong rebukes of Sea Shepherd's tactics from the strongly anti-whaling governments of Australia and New Zealand.

The newly named Steve Irwin will form the backbone of Sea Shepherd's Antarctic mission.

Sea Shepherd founder Paul Watson said the television star shared the group's passion for saving whales.

"Steve wanted to come to Antarctica with us to defend the whales, and now he will be joining us in spirit with his name emblazoned" on the ship, Watson said in a statement.

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